The Simulation Of Ecological Water Level Operation In Hanfeng Lake

Today,water ecological environment is a hot topic,and it is also the subject of various research projects.The study object of water ecological environment is river,lake,reservoir,etc.,and its study field involved aquatic ecological（fish,algae,etc.）,terrestrial ecosystem（the water-level fluctuation belt）,and water environment（water quality）.As construction and put into operation of some water conservancy project（brake,weir dam,hydropower station,etc.）,there were some problems in water ecological environment becoming more obvious,such as decreasing sharply of fish resource,increasing of bare area in water-level-fluctuation zone,and eutrophication,especially Han Feng lake as the representative of the river-type lake among others,and as one of the tributaries of the Three Gorges upstream,water ecological and environment were affected seriously by level change of the Three Gorges.Water level regulating dam has turned Han Feng Lake into“main-vice reservoirs”,changed the hydrological conditions,blocking the migration routes of the rheophilic fish,water level fluctuation influence the recovery of wetland landscape pattern,and there were an increase of nutrient in different areas by the infusion of farmland irrigation water and municipal sewage,this is the reasons why different regions present different degree of eutrophication.How to improve the water ecological environment condition of such river-type lake is an important scientific project that have to be settled urgently in our country.Therefore,aiming at the characteristic of Han Feng lake,summarizing the water level regulation demand for improving water ecological environment according to the investigation and analysis of aquatic ecological conditions（algae,fish habitat,wetland landscape pattern of water-level-fluctuation zone）and water environment conditions（eutrophication and driving factors）,then establish the two-dimensional hydrodynamic and water quality coupled model to simulating different water quantity operation schemes,and the comprehensive technology research with the improvement of fish habitat,the recovery of wetland landscape pattern in water-level-fluctuation zone,the prevention and control of algae and eutrophication could make a contribution to ecological response theory and practice of aquatic ecological conservation and water environment governance in river-type lake.In order to study the eutrophication driven factors and its status in Han Feng Lake,exploratory data analysis were applied to analyze the relationship between hydrodynamic conditions and environmental factors,the principal component of water quality,the related environmental factors of entropy weight and NHI（Nutritional Health Index）.The results of regression analysis show that a positive correlation between water level and transparency,and negative correlations among flow discharge and DO,Chla,CODMn,NH₄⁺-N and DTP;three principal component were extracted by Principal Component Analysis（PCA）,which represented nutrients,organic pollutants and algae,respectively.The entropy weights of DO,TN,TP show that the eutrophication status of Han Feng lake were subjected to aerobic organic pollutants,nitrogen and phosphorus.The nutritional health index show that S1>S3>S6（the center of lake）>S7（the tail of lake）>S5（the head of lake）>S4>S2.In general,the eutrophication level of Han Feng lake was ranged from mesotropher to light eutropher,with higher nutrient levels in South river,and higher nutrient in the center of lake when compare to the head and the tail of lake.In conclusion,reducing the input of organic pollutants and nutrient,and improving the hydrodynamic conditions of the local area are able to efficiently inhibit the growth of algae,which favors to the control of eutrophication.Based on the analysis of response relationship between basic parameter of wetland landscape pattern,the fragmentation index and water level,it’s beneficial to the recovery of wetland landscape pattern when running water level changed between 166.50 m and 168.50 m and could be reduce the negative influence by the change of water level,as the change of fragmentation is minimal and the protective effect of species is better.By investigating the current situation of fish resource,the water level regulation of Han Feng lake were blocked the migration routes,and make it lost the flow pulsation that contribute to stimulating the fish spawning of drifting eggs.The weakening of the dynamic condition in Han Feng lake is not enough to meet the demand for developing of some floating eggs,and only just the current speed over 0.2m/s could satisfied for growing of drifting eggs.In order to study the influence of regulating dam’s water quantity operation in Han Feng lake on the hydropower and water eutrophication in reservoir region,MIKE21 were employed to build two-dimension hydrodynamic and transport model based on the data of flow rate,water level and water quality measured in 2014,the accuracy of the model was verified by using the measured data of current speed,TN and TP.Based on the demand of fish habitat,the recovery of wetland landscape pattern in water-level-fluctuation zone,the prevention and control of algae and eutrophication for water level and hydrodynamic conditions in Han Feng lake,7 kinds of water quantity operation schemes were designed by applying the scenario analytical methods,according to the established two-dimensional hydrodynamic model,7 different schemes were simulated to explore the distribution tendency of current speed,TN and TP.Comparing the operation conditions of all schemes showed that water regulating mode with large quantity increased effectively the current speed in reservoir region,and decreased the concentration of TN and TP in a short period,However,more longer operation time was required to decrease the nutrient concentration in the whole region The research provided scientific basis for managing the water operation of regulating dam and controlling eutrophication in Han Feng lake.